The Q document, also called the Q Gospel, the Sayings Gospel Q, the Synoptic Sayings Source, and in the 19th century the
Logia, comprises a hypothetical collection of Jesus' sayings, hypothesized in accordance with the two-source hypothesis to be a source of the Gospels of Matthew and Luke. The symbol Q comes the first letter of the German word for source, Quelle.

The two-source hypothesis forms the most widely accepted solution to the synoptic problem, which posits that Matthew and Luke drew on two written sources, as shown by textual correspondences between their works. The Gospel of Mark forms one source, and Q the other.

The Case for Q

The existence of Q follows from the argument that Matthew and Luke show independence in the double tradition,
the material that Matthew and Luke shared that does not appear in Mark. Accordingly, the literary connection in the double tradition is explained by an indirect relationship, namely, through use of a common source or sources.

Arguments for Luke's and Matthew's independence include:

Matthew and Luke have different contexts for the double tradition material. It is argued that it is easier to explain Luke's "artistically inferior" arrangement of the double tradition into more primitive contexts within his Gospel as due to not knowing Matthew.

The form of the material sometimes appears more primitive in Matthew but at other times more primitive in Luke.

Independence is likely in light of the non-use of the other's non-Markan tradition, especially in the infancy, genealogical, and resurrection accounts.

Doublets. Sometimes it appears that doublets in Matthew and Luke have one half that comes from Mark and the other half from some common source, i.e. Q.

Even if Matthew and Luke are independent, the Q hypothesis states that they used a common
document. Arguments for Q being a written document include:

There is commonality in order between the two Sermons on/at the Mount.

The presence of doublets, where Matthew and Luke sometimes present two versions of a similar saying, but in different contexts. Doublets often serve as a sign of two written sources.

Certain themes, such as the Deuteronomistic view of history, are more prominent in Q than in either Matthew or Luke individually.

History

If Q ever existed, it must have disappeared very early, since no copies of it have been recovered and no definitive notices of it have been recorded in antiquity (but see the discussion of the Papias testimonium below).

In modern times, the first person to hypothesize a Q-like source was an Englishman, Herbert Marsh, in 1801 in a complicated solution to the synoptic problem that his contemporaries ignored. Marsh labeled this source with the Hebrew letter
beth.

The next person to advance the Q hypothesis was the German Schleiermacher in 1832, who interpreted an enigmatic statement by the early Christian writer Papias of Hierapolis, circa 125: "Matthew compiled the oracles (Greek: logia) of the Lord in a Hebrew manner of speech." Rather than the traditional interpretation that Papias was referring to the writing of Matthew in Hebrew, Schleiermacher believed that Papias was actually giving witness to a sayings collection that was available to the Evangelists.

In 1838, another German, Christian Hermann Weisse, took Schleiermacher's suggestion of a sayings source and combined it with the idea of Markan priority to formulate what is now called the Two-Source Hypothesis, in which both Matthew and Luke used Mark and the sayings source. Heinrich Julius Holtzmann endorsed this approach in an influential treatment of the synoptic problem in 1863, and the Two-Source Hypothesis has maintained its dominance ever since.

At this time, Q was usually called the Logia on account of the Papias statement, and Holtzmann gave it the symbol Lambda
(Λ). Toward the end of the 19th century, however, doubts began to grow on the propriety of anchoring the existence of the collection of sayings in the testimony of Papias, so a neutral symbol Q (which was devised by Johannes Weiss based on the German Quelle, meaning source) was adopted to remain agnostic on the collection of sayings and its connection to Papias.

In the first two decades of the 20th century, more than a dozen reconstructions of Q were made. However, these reconstructions differed so much from each other that not a single verse of Matthew was present in all of them. As a result, interest in Q subsided and it was neglected for many decades.

This state of affairs changed in the 1960s after translations of a newly discovered and analogous saying collection, the Gospel of Thomas, became available. James M. Robinson and Helmut Koester proposed that collections of sayings such as Q and Thomas represented the earliest Christian materials at an early point in a trajectory that eventually resulted in the canonical gospels.

This burst of interest led to increasingly more sophisticated literary and redactional analyses of Q, notably the work of John S. Kloppenborg. Kloppenborg, by analyzing certain literary phenomena, argued that Q was composed in three stages. The earliest stage was a collection of wisdom sayings involving such issues as poverty and discipleship. Then this collection was expanded by including a layer of judgmental sayings directed against "this generation". The final stage included the Temptation of Jesus.

Although Kloppenborg cautioned against assuming that the composition history of Q is the same as the history of the Jesus tradition (i.e. that the oldest layer of Q is necessarily the oldest and pure-layer Jesus tradition), some recent questers after the Historical Jesus, including the Jesus Seminar, have done just that. Basing their reconstructions primarily on the Gospel of Thomas and the oldest layer of Q, they propose that Jesus functioned as a wisdom sage more analogous to a Greek
Cynic philosopher than to a Jewish rabbi.

Cynic: an adherent of an ancient Greek school of philosophers who held the view that virtue is the only good and that its essence lies in self-control and
independent thinking.